VK Callback API and SSL certificate. How?

Question

linux

Set up Callback API.
My server responds to requests from VK. Everything is OK.
Next, I generated a certificate and exported it to PKCS # 12. Loaded it in the API settings.
The certificate from StartSSL is already installed on its server (the site is spinning on it).
The instructions say:

"You also need to further configure your server to be able to authenticate using the client certificate you created earlier."

But I already have lines in Apache that tell me to use the StartSSL certificate.
How can I force Apache to use the vkapi.crt certificate when requesting the ./callback/vk.php file? And at the same time, comply with the requirement of everything from the same instructions:

"Please note! Your server must have a root SSL certificate signed by an authorized certification authority. A self-signed root certificate is not enough to work with the Callback API."

By the way, even in the current situation, the request from VK is processed by my server without errors. It seems that the certificate is not used, although it is uploaded to VK.

Answer 1

You need to configure authentication using a client certificate, see here for details: https://www.opennet.ru/base/sec/ssl_cert.txt.html
Only anyone can forge a request to your server.